Solar dish concentrator with a molten salt receiver incorporating thermal energy storage

ABSTRACT

A solar power system capable of storing heat energy and converting sun light to electrical power. The solar power system includes a solar collection system which gathers and transmits concentrated solar energy to an absorber/cavity. The thermal energy is extracted from the absorber/cavity via a fluid and transported to a heat conversion system. The heat conversion system uses the thermal energy to create electricity.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of electrical energygeneration through solar power collection, and more particularly, toelectrical energy generation using an absorber with solar dishconcentrators and a molten salt receiver with thermal storagecapability.

BACKGROUND OF THE INVENTION

[0002] The desire to decrease and ultimately eliminate dependence onfossil fuels has stimulated research into clean and renewable ways toproduce electricity for the global marketplace. Solar power has become aviable option because it is a clean form of energy production and thereis a potentially limitless supply of solar radiation. To that end, it isestimated the solar energy flux from the sun is approximately 2.7megawatt-hours per square meter per year in certain advantageous areasof the world. With this tremendous amount of free and clean energyavailable, and the desire to reduce dependence on fossil fuels, solarpower production is now, more than ever, being reviewed as an importantmeans to help meet the energy consumption demands in various parts ofthe world.

[0003] Technological innovations and improvements have helped to maketerrestrial solar power generation a feasible means for large scalepower production. More specifically, the reduction in the magnitude ofcapital investment required and the reduction in recurring operation andmaintenance costs allow solar power generation to compete with otherforms of terrestrial power generation. Further, the scalability of solarpower plants has the potential to enable smaller facilities to beconstructed, with production capacity on the order of ten kilowatts, forcommunities with smaller demands, and larger facilities, capable ofproducing one hundred megawatts or more, for large metropolitan areaswith higher energy demands.

[0004] To address the above demand for solar power systems manyconfigurations have been designed and implemented. One suchimplementation is a concentrated solar power system that collects solarenergy and concentrates that energy onto an absorber. The absorbedoptical energy is carried away from the absorber by a fluid, for examplemolten salt, and then pumped to a power conversion system. The powerconversion system then produces electricity that is eventually fed intothe national electrical grid. After the fluid leaves the powerconversion system it is then pumped back to the absorber.

[0005] A typical concentrated solar power system uses a fluid totransport absorbed heat energy from a heat receiver to aheat-to-electricity conversion system. A fluid with significant thermalcapacitance, typically molten salt, is used to allow storing collectedenergy as sensible heat in the fluid. The ability to store energy allowsseparating the energy collection and energy production functions so thatenergy can be produced during periods of high demand, even nighttime,while energy collection is conducted when sufficient sunlight isavailable. This significantly enhances the economics of the power plant.The energy collection typically includes a central receiver/absorbersurrounded by a large field of heliostats. The central receiver istypically a tall cylindrical tower made up of multiple absorber tubes.The heliostats intercept the incident solar energy and reflect it to theabsorber tubes making up the receiver tower. The reflected energy isabsorbed on the absorber tubes while molten salt flowing on the insideof the tubes is used to transport the absorbed energy effectivelycooling the absorber tubes. The energy contained in the molten salt, assensible heat, can then be used to drive a heat engine. Although thissystem has the advantage of thermal energy storage via the molten salt,the system has low energy collection efficiency due to inefficiencies inthe heliostat optical system and from heat losses off the large open-airreceiver/absorber. Conversely, point focus solar power systems,typically using a parabolic dish concentrator coupled to an absorbercavity, have high solar energy collection efficiency and are capable ofachieving higher temperatures. However, typical implementation of thissystem provides direct conversion of the absorbed energy to electricityvia a thermal engine, for example a Stirling engine, coupled directly tothe absorber cavity. There is no energy storage capability, therefore,the economics of this system suffer because the energy production cannotbe optimized to follow the energy demand.

[0006] Accordingly, a need exists for a solar power generation systemcapable of efficient energy collection, with high temperaturecapability, and with the ability to store collected energy so thatelectrical energy production can be optimized to follow periods of highpower demand.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a solar power system capableof storing heat energy wherein sun light is converted to electricalenergy. The solar power system includes a solar collection system andpower conversion system. The solar collection system has a concentratorwhich reflects the sunlight onto an absorber. The concentrated sunlightenters the absorber through an aperture and warms a receiving cavityinside the absorber. A heat exchanger is coupled to the absorber andtransfers the heat from the receiving cavity to a fluid.

[0008] The power conversion system has a pump system which circulatesthe fluid. A first pump impels the fluid from a cold storage tank to theheat exchanger/absorber. The heat exchanger transfers the thermal energyfrom the sunlight to the fluid. A hot storage tank receives the fluidfrom the heat exchanger/absorber. A second pump pumps the fluid to theheat engine and then back to the cold fluid reservoir. The heat engineconverts the heat to electricity.

[0009] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specific examplesare intended for purposes of illustration only and are not intended tolimit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

[0011]FIG. 1 is a schematic of a solar power system according to apreferred embodiment of the present invention;

[0012]FIG. 2 is a sectional perspective view of the solar power systemof FIG. 1 along line 2-2; and

[0013]FIG. 3 is a schematic of a solar power system having multiplecollection systems according to the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

[0015] With reference to FIG. 1, a solar power system 10 in accordancewith a preferred embodiment of the present invention is shown. The solarpower system 10 includes a solar collection system 12. The solarcollection system 12 gathers sunlight 14 and concentrates the sunlight14 before transmitting the solar energy from the sunlight 14 to a powerconversion system 16. The power conversion system 16 uses the thermalenergy from the solar collection system 12 to create electricity.

[0016] The solar collection system 12 has a solar concentrator system18. The solar concentrator system 18 gathers sunlight 14 andconcentrates the sunlight 14 before transferring the solar energy fromthe sunlight 14 to an absorber system 20.

[0017] The solar concentrator system 18 includes a mirror 22. In onepreferred form, the mirror 22 is generally dish-shaped and parabolic.The sunlight 14 strikes the mirror 22 and is reflected to a focus 24 ofthe mirror 22. The mirror 22 is coupled to a support structure 26 thatsupports the mirror 22. The support structure 26 is further coupled to apivot assembly 28. The pivot assembly 28 is rotatably coupled to a base30. The base 30 is affixed to a ground surface as shown. The pivotassembly 28 enables the mirror 22 to be adjusted to track the sun as thesun travels across the sky. Specifically, the pivot assembly 28 providestwo axes of rotation for the mirror 22, as known in the art. Acontroller 32 coupled to the solar concentrator system 18 controls thepivot assembly 28 so that it causes the mirror 22 to track the sunacross the sky. More specifically, the controller 32 drives a motor (notshown) associated with the pivot assembly 28 to pivot mirror 22 asneeded.

[0018] The sunlight 14 is reflected from the solar concentrator system18 to the absorber system 20 as shown in FIG. 2. The concentratedsunlight 14 enters the absorber system 20 through an aperture 34therein. The reflected sunlight 14 passes through the aperture 34 into areceiving cavity 36. The receiving cavity 36 is lined with an absorptivematerial 38. The absorptive material 38 absorbs the solar energy andaids in the distribution of the resulting thermal energy to a pluralityof heat exchanger tubes 40. The absorptive material 38 may include, forexample, castable refractory brick, graphitic absorbers or heat pipeabsorbers. The heat exchanger tubes 40 are of the radiantabsorber-to-liquid type and, in this embodiment, are preferablyconstructed of Inconel® alloy or other suitable alloys, and may beconfigured as a straight or coiled tube. The heat exchanger tubes 40receive the thermal energy from the absorption of concentrated sunlight14 and transfer the energy into a fluid 42. The fluid 42 is retained andflows within the heat exchanger tubes 40. In this embodiment, the fluid42 is a 60/40 mixture of sodium and potassium nitrate, however, thefluid 42 could also be a liquid metal such as, for example, sodium,lithium, or potassium. The heat exchanger tubes 40 are surrounded by aninsulation layer 48 that reduces heat loss to the atmosphere. Inparticular, high wind speed contributes to heat loss, as the high windsproduce convective losses. The insulation layer 48, however, enables theheat exchanger tubes 40 to maintain temperature even if the sunlight 14has diminished or the heat exchanger tubes 40 are exposed to high winds.The insulation layer 48 may include for example, microtherm or othersimilar form of bulk insulation.

[0019] In addition, the aperture 34, receiving cavity 36 and heatexchanger tubes 40 can be shielded with conventional heat protectors(not shown). The heat protectors allow the aperture 34, receiving cavity36 and heat exchanger tubes 40 to withstand transient misalignments ofthe mirror 22 due to winds and operational vibration. Thus, if the focus24 not aimed directly at the receiving cavity 36, it will not burn ormelt the aperture 34, receiving cavity 36 or heat exchanger tubes 40.

[0020] The fluid 42 of the absorber system 20 transports thermal energyto the power conversion system 16. The power conversion system 16receives thermal energy from the solar collection system 12 via thefluid 42. The power conversion system 16 includes a conversion engine 46and a pump system 50. The fluid 42 from the solar collection system 12is transported to the conversion engine 46 via the pump system 50.

[0021] The pump system 50 circulates the fluid 42 through both the solarcollection system 12 and the power conversion system 16. The pump system50 has a cold storage system 52 and a hot storage system 56. The coldstorage system 52 provides cooled fluid 42 at a temperature ofpreferably about 550° C. (1022° F.) to the solar collection system 12for heating. The cold storage system 52 includes a first pump 54. Thefirst pump 54 is a centrifugal pump which pumps cooled fluid 42 from acold storage tank 58 into the absorber system 20. The hot storage system56 collects and stores hot fluid 42′ from the absorber system 20 andsupplies hot fluid 42′ at a temperature of about 600° C. (1122° F.) tothe power conversion system 16. As the hot fluid 42′ exits the absorbersystem 20, it flows into a hot storage tank 60 of the hot storage system56. The hot storage tank 60 may be modified to increase the thermalcapacity by, for example, placing rocks therein. The hot fluid 42′ isremoved from the hot storage tank 60 by a second centrifugal pump 62.

[0022] In this embodiment, the first and second pumps 54, 62 arecommercially available fluid pumps. One source is Nagle Pumps, Inc. ofChicago Heights, Ill. The first pump 54, pumps the fluid 42 at a flowrate commensurate with the current solar condition. The secondcentrifugal pump 62, pumps the fluid 42 consistent with the heat demandof the power conversion system 16. The first pump 54 and secondcentrifugal pump 62 receive control inputs from a controller 66. Thecontroller 66 determines if the first pump 54 should operate based uponthe output of a solar sensor 67 and upon the output of temperaturesensors (not shown) located in or around the receiving cavity 36. Thetemperature sensors measure the temperature of the hot fluid 42′ at theexit of the receiving cavity 36. If the controller 66 determines a solarpower generation condition exists (i.e. the sun is out), the controller66 enables the first pump 54. The first pump 54 then pumps the coldfluid 42 into the absorber system 20 for heating. The controller 66 alsodetermines if the second centrifugal pump 62 should be enabled basedupon the present power demand. If the controller 66 receives a signalindicating a high demand for power, the controller 66 enables the secondcentrifugal pump 62 to pump the hot fluid 42′ from the hot storage tank60 into the conversion engine 46.

[0023] The conversion engine 46 uses the thermal energy to createelectricity. The conversion engine 46 may comprise any engine capable ofconverting thermal energy into electricity, such as, for example, aStirling engine, a Rankine engine or a Brayton engine. In applicationsrequiring low scale energy productions, a Stirling engine would be mostsuitable. Conversely, in large scale production, a Rankine engine wouldbe more desirable.

[0024] The waste heat from the power conversion system 16 is removed bya cooling water system 68. The cooling water system 68 consists of acooling water supply 70 and a cooling water return 72. The cooling watersystem 68 provides the cooling water at a flow rate necessary to removethe waste heat from the power conversion system 16 with a temperaturerise commensurate with the cooling water utility being employed.

[0025] Alternatively, the solar power system 10 can be constructed withmultiple solar concentrator systems 18 as shown in FIG. 3. The long rowsof solar concentrator systems 18 are constructed with the absorbersystems 20 disposed above them (not shown). A conduit 74 transports thefluid 42 to the power conversion system 16. A fired heater 76 may beadded to facilitate startup and allow operation during periods ofreduced solar insulation or to augment solar energy to accommodate powerpeaking requirements. One skilled in the art will readily appreciatethat the solar power system 10 can be scaled to accommodate a wide rangeof demands for solar power.

[0026] In operation of the solar power system 10, if a solar powergeneration condition exists, the sunlight 14 strikes the mirror 22 ofthe solar concentrator system 18. The mirror 22 concentrates thesunlight 14 to the focus 24, which is essentially at the aperture 34.The sunlight 14 passes through the aperture 34 into the receiving cavity36. The solar energy collected in the receiving cavity 36 is absorbedand the resulting thermal energy is transferred into the fluid 42 by theheat exchanger tubes 40. Simultaneously, the first pump 54 is pumpingcool fluid 42 from the cold storage tank 58 into the absorber system 20.Upon receiving thermal energy via the heat exchanger tubes 40, the now,hot fluid 42′ flows into the hot storage tank 60. If the controller 66determines that a high power demand exists, the second centrifugal pump62 pumps the hot fluid 42′ into the conversion engine 46. The conversionengine 46 uses the thermal energy from the hot fluid 42′ to generateelectricity. The now cooled fluid 42 exits the conversion engine 46 andreturns to the cold storage tank 58. This process will repeat as long asa solar power generation condition exists as determined by thecontroller 66.

[0027] If a solar power generation condition does not exist, electricitycan still be generated for a high power demand condition. In thissituation, the solar power system 10 will perform as previouslydiscussed with the exception that the first pump 54 will not operate topump cool fluid 42 into the absorber system 20. Hence, the only thermalenergy available to the solar power system 10 is that in the hot storagetank 60. Conversely, if a solar power generation condition exists,thermal energy will still be generated and stored in preparation for ahigh power demand condition. In this situation, the the secondcentrifugal pump 62 will not be operated. The hot fluid 42′ would thenremain in the hot storage tank 60.

[0028] The solar power system 10 provides efficient collection of solarenergy while being capable generating a higher temperature than currentcentral receiver systems, resulting in a solar power system 10 that ismore efficient than current central receiver systems. Additionally, thesolar power system 10 has the ability to store the collected energy sothat solar collection and electrical energy production functions can beseparated and optimized. This enables the solar power system 10 toproduce power according to the demand conditions which significantlyimproves the economic viability of current dish type systems, producingelectricity at fewer dollars per kilowatt-hour than typical solar powersystems.

[0029] The description of the invention is merely exemplary in natureand, thus, variations that do not depart from the gist of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A solar power system capable of storing heatenergy wherein sun light is converted to electrical energy comprising: alight conversion system having an absorber and a concentrator, saidabsorber having a heat exchanger, an aperture, and a receiving cavity;said concentrator having a mirror and a sun-tracking system; saidconcentrator reflects the sun light into said absorber through saidaperture, wherein the sun light warms said receiving cavity disposedwithin said absorber; said heat exchanger transfers heat from saidreceiving cavity to a fluid; a heat conversion system having a hotsegment and a cold segment; said cold segment having said heatexchanger, a cold fluid hold, and a cold fluid pump; said hot segmenthaving a hot fluid hold, a hot fluid pump and a heat engine; said hotfluid hold receives said fluid from said heat exchanger; said hot fluidpump impels said fluid to said heat engine and then to said cold fluidhold, wherein said heat engine converts heat to electricity; said coldfluid pump impels said fluid from said cold fluid hold to said heatexchanger then to said hot fluid hold, wherein said heat exchangertransfers the heat to said fluid; said hot segment operates under apower-demand condition; and said cold segment operates under a sunlightcondition.
 2. A solar power system of claim 1, wherein said aperture issized to reduce heat loss from said absorber.
 3. A solar power system ofclaim 1, wherein said fluid is a mixture of Sodium and PotassiumNitrate.
 4. A solar power system of claim 1, wherein said fluid is oneof Lithium, Sodium, and Potassium.
 5. A solar power system of claim 1,wherein said heat engine is one of a Steam Rankine engine, an OrganicRankine Engine, a Stirling Engine and a Brayton Cycle Engine.
 6. A solarpower system of claim 1, wherein additional thermal capacitance can beadded to said hot fluid reservoir to increase thermal storagecapability.
 7. A solar power system of claim 1, wherein said heatexchanger is constructed of Inconel.
 8. A solar power system of claim 1,wherein said concentrator is a dish-shaped parabolic.
 9. A solar powersystem of claim 1, wherein said fluid resides in said hot fluidreservoir at 600° C.
 10. A solar power system of claim 1, wherein saidfluid resides in said cold fluid reservoir at 550° C.
 11. A solar powersystem of claim 1, wherein said power demand condition can occur duringperiods without sun light.
 12. A solar power system of claim 1, whereinsaid receiving cavity is coated with graphite or highly absorptive paintto increase solar absorption.
 13. The solar power system of claim 8,wherein said dish concentrator reflects the sun light into a pointfocus.
 14. The solar power system of claim 13, wherein said point focusis aligned with said aperture in said absorber.
 15. A solar power systemcapable of storing heat energy wherein sun light is converted toelectrical energy comprising: an absorber having a receiver cavity, anaperture and a heat exchanger, said aperture disposed within a wall ofsaid cavity and allowing the sun light to pass into said receivercavity, said heat exchanger disposed within said receiver cavity,wherein the sun light passes through said aperture and contacts saidheat exchanger, wherein said heat exchanger absorbs the heat energy fromthe sun light, wherein said heat exchanger has a hot end and a cold end;a dish concentrator that reflects the sun light into a focus having asun-tracking system to maintain said dish concentrator aligned with thesunlight; a hot fluid reservoir storing a fluid at a hot-routetemperature, said hot fluid reservoir is fluidly connected to said hotend of said heat exchanger; a first fluid pump, wherein said first fluidpump impels said fluid from said hot fluid reservoir to a powerconversion system; said power conversion system extracts the heat energyfrom said fluid and converts the heat energy to electrical energy,wherein said fluid enters said power conversion system at said hot-routetemperature and exits at a cold-route temperature; a cold fluidreservoir storing said fluid at said cold-route temperature; said coldfluid reservoir is fluidly connected to the power conversion system; asecond fluid pump, wherein said second fluid pump impels said fluid fromsaid cold fluid reservoir to said cold end of said heat exchanger. 16.The solar power system of claim 15, wherein said dish concentratorreflects the sun light into a point focus.
 17. The solar power system ofclaim 15, wherein said focus is aligned with said aperture in saidabsorber.
 18. A solar power system of claim 15, wherein said aperture issized to reduce heat loss from said absorber.
 19. A solar power systemof claim 15, wherein said fluid is a mixture of Sodium and PotassiumNitrate.
 20. A solar power system of claim 15, wherein said powerconversion system is one of a Steam Rankine engine, an Organic RankineEngine, a Stirling Engine and a Brayton Cycle Engine.
 21. A solar powersystem of claim 15, wherein additional thermal capacitance can be addedwithin said hot fluid reservoir to increase thermal storage capability.22. A solar power system of claim 15, wherein said heat exchanger isconstructed of Inconel.
 23. A solar power system of claim 15, whereinsaid hot-route temperature is about 600° C.
 24. A solar power system ofclaim 15, wherein said cold-route temperature is about 550° C.
 25. Asolar power system of claim 15, wherein said receiving cavity is coatedwith graphite or highly absorptive paint to increase absorption.
 26. Amethod for removing and storing heat energy from sun light and thenconverting the heat energy to electrical energy comprising the steps of:providing plurality of dish concentrators to reflect the sun lightthrough a plurality of apertures into a plurality of absorber cavitiesthe sunlight heating a heat exchanger in said absorber cavity; aligningsaid plurality of dish concentrators with the sun light; impelling afluid from a cold fluid hold to said heat exchangers, heating said fluidto a hot-route temperature, and impelling said fluid from said heatexchangers to a hot fluid hold when a sunlight condition exists; andimpelling said fluid from said hot fluid hold to a power conversionsystem, generating electricity, and impelling said fluid at a cold-routetemperature to said cold fluid hold, when a power demand conditionexists.